[tahtawy]

Hi guys
I am simulating charging a tank by heat pipe at bottom

Geometry :
when I did the geometry to separate the fluid in the tank from the fluid in the pipe I just made on sketch with rectangle >> surface from sketch >> another sketch have the pipe >> Face split to split sketch 2 from surface 1

Model setup: Bcs
1) walls of tank : I put expression for heat flux which represents the loss to the surroundin
2) Inlet to pipe : mass flow inlet with 0.05 kg/s
3) Outlet from pipe : outflow
4) top wall of pipe and its shadow : Coupled / copper
5) bottom wall of pipe and its shadow : Coupled / copper

Problem is
whenever I do the simulation the mass flow rate of both inlet and outlet drop to 0.026

so I don't know exactly where is the problem ???

[vinerm]

The description you have shared is not clear. Could you share a few images to clarify?

[tahtawy]

dear Mr Vinerm,
Thanks for your help

[tahtawy]

to be continued

[tahtawy]

here are the rest

[tahtawy]

The describtion:
Water at tank is initially at 20 degree C
and Mass flow rate to the pipe is 0.05 kg/s and its temp is 60 degree c
That is the all know
So it is charging the tank from bottom so the tank will be mixed

My problem
1) When the first iterations are preformed the mass flow rate become 0.026 instead of defined fixed rate of 0.05

2) The curve of outlet temp of the pipe is not smooth and this gives me nonj other smooth results but the paper I compare with has very smooth curves

Please help

[vinerm]

Two things need to be changed.

1. Change outlet condition from outflow to pressure outlet.
2. Use a time-step smaller than 1 s. 1 s is very large time-step for this simulation

Furthermore, you are using Boussinesq for water density, however, you also need to ensure that the operating conditions, i.e., operating pressure, Boussinesq Temperature, Operating Density, and reference location for the operating pressure are correct.

[tahtawy]

Thanks for reply

1) The outlet from the pipe is supposed to go through a cycle which is not mentioned in the paper and not mentioned its pressure so what should I do about that ?

2) so what does the large step probably cause ? unsmoothness of the curve or wrong results?

3) Where i can find those operating conditions in fluent , I never used them

[vinerm]

1. What is implied by a cycle? Is it a closed circuit for water? Then you need most likely not need to include it here because inlet would be based on what happens in the section where water is heated. So, most likely, this part is alright.

2. Time-step causes multiple changes. First, the simulation needs to be converged in each time-step. For a time-step of 1 s, this might require more than 30-40 iterations per time-step. This is akin to drawing a hexagon or octagon and calling it a circle. Numerical stability and physical accuracy, both are affected.

3. Operating conditions are available in the middle column when you double click on either Boundary Conditions or Cell Zone Conditions on the left column.